The IP host address, or more commonly just IP address, is used to identify hosts connected to the Internet. IP stands for Internet Protocol and refers to the Internet Layer of the overall network architecture of the Internet. An IP address is a 32-bit quantity interpreted as 4 8-bit numbers or octets. Each IP address uniquely identifies the participating user network, the host on the network, and the class of the user network.

An IP address is usually written in a dotted-decimal notation of the form N1.N2.N3.N4, where each Ni is a decimal number between 0 and 255 decimal (00 through ff hexadecimal). Addresses are controlled and assigned by the Internet Network Information Center at SRI International. There are currently 5 defined classes of networks, called A, B, C, D and E; classes A, B and C are available to users. Each interface on a host system connected to the Internet must have its own IP address.